This invention relates generally to a seat suspension apparatus for resiliently supporting the operator's seat on off-highway vehicles such as tractors and the like. More particularly, the invention comprises an improved hydraulic system having a hydraulic cylinder for supporting the seat, fluid receiving means for providing cushioned, impact-attenuating seat support and means for adjustably dampening fluid flow rates between the cylinder and the fluid receiving means. An adjustable metering valve is provided within the cylinder for automatically positioning the seat to a preselected reference height which is independent of the weight of the operator.
Such vehicles are usually operated upon rough terrain and unless minimized, the resulting impact to the seated operator impairs vehicle control and increases operator fatigue. The controllability of the vehicle is enhanced and operator fatigue is further reduced if the height of the seat is adjustable to conform to the physical characteristics of a particular operator. Prior art devices for resiliently supporting seats at an adjustable height and for attenuating the severity of such impact include motion dampening resilient springs of the leaf, coiled or air variety and are sometimes used in conjunction with conventional automotive shock absorbers. Adjustment of seat height is usually accomplished by providing means for manipulating the entire platform upon which the seat support system is mounted. When such springs are selected to have a low spring rate and provide optimum impact dampening upon downward seat movement, the resulting time required to return the seat to a reference height is undesirably increased. Conversely, if springs having a high rate are selected for optimum time of return to a reference height, the impact dampening characteristics upon downward seat movement become unnecessarily harsh. While these prior art devices have heretofore provided satisfactory means for supporting and cushioning seats on off-highway vehicles, the resulting motion dampening characteristics are undesirably uniform for either direction of seat movement relative to the supporting vehicle. Additionally, their mechanisms for adjusting seat height are often comprised of multiple part mechanical linkages which are cumbersome and difficult to operate. Accordingly, a system which provides resilient, cushioned seat support at an easily adjustable height independent of operator weight and which provides for adjustable motion dampening characteristics which are optimized for either direction of seat movement would be a significant advance over the prior art.